COLORLESS MONOCHLOROACETIC ACID AND THE METHOD OF PREPARATION THEREOF

Abstract

An improved method of producing monochloroacetic acid (MCAA) is disclosed, which affords a colorless monochloroacetic acid product in any form that can be obtained by this method.

Claims

1. A method for producing a colorless monochloroacetic acid, comprising a crude monochloroacetic acid peroxidation step, wherein the peroxycarboxylic acid, preferably peracetic acid, is added to the crude monochloroacetic acid in liquid form in an amount of at least 50 ppm based on the weight of the crude monochloroacetic acid and the peroxidation reaction is carried out at a temperature of 20° C. to 100° C. until a colorless product with a color level below 100 units on Hazen scale is obtained, then, if necessary, cooled to room temperature, optionally added with water and packed, wherein a pure monochloroacetic acid in molten form or a water-diluted monochloroacetic acid with a concentration above 60 wt %, preferably the water-diluted monochloroacetic acid with a concentration from 60% wt % to 90 wt % is used as crude monochloroacetic acid.

2. The method according to claim 1, wherein the peroxycarboxylic acid is peracetic acid.

3. The method according to claim 1, wherein the peroxycarboxylic acid is used in the form of an aqueous solution with a concentration of 10% to 25% of the peroxycarboxylic acid.

4. The method according to claim 1, wherein the peroxycarboxylic acid is used in an amount of 50-1000 ppm based on the weight of the pure monochloroacetic acid, preferably 100-500 ppm, most preferably 100-300 ppm.

5. The method according to claim 1, characterized in that the peroxycarboxylic acid is used in an amount of 50-1000 ppm based on the weight of the diluted monochloroacetic acid, preferably 50-500 ppm, most preferably 50-100 ppm.

6. The method according to claim 1, comprising the peroxidation process is carried out at a temperature of 20° C. to 100° C., preferably at a temperature of 70-100° C. for undiluted monochloroacetic acid, and 20-80° C. in the case of water-diluted monochloroacetic acid.

7. The colorless monochloroacetic acid, wherein it maintains a coloration of less than 60 units on Hazen scale for at least 7 days when stored at a temperature of not more than 70° C.

8. The monochloroacetic acid according to claim 7, wherein it has a form selected from: 100% monochloroacetic acid in solid form, preferably flakes, 100% monochloroacetic acid in molten form, or water-diluted monochloroacetic acid with a concentration of 60 wt % to 90 wt % in liquid form.

9. The monochloroacetic acid according to claim 7, wherein it has been obtained by a method according to claim 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0032] The invention relates to a method for preparing a permanently colorless monochloroacetic acid, in any product form, comprising a step after distillation and/or before packaging and/or before diluting the monochloroacetic acid with water by thermally stabilizing the trace impurities by peroxidating them with peroxycarboxylic acid in order to ensure the inertness of organic impurities sensitive to high temperature, which are responsible for accelerating the aging of the final products, i.e. monochloroacetic acid in the molten form, monochloroacetic acid in the solid form, monochloroacetic acid diluted with water at a concentration of 60-90%, which is manifested by an increase in the color of the product.

[0033] Preferably, the peroxycarboxylic acid is peracetic acid.

[0034] Preferably, the peroxycarboxylic acid is in the form of an aqueous solution with a concentration of 10% to 25%.

[0035] Preferably, the peroxycarboxylic acid is used in an amount of 50-1000 ppm based on the weight of pure monochloroacetic acid, preferably 100-500 ppm, most preferably 100-300 ppm.

[0036] Preferably, the peroxycarboxylic acid is used in an amount of 50-1000 ppm based on the weight of the dilute monochloroacetic acid, preferably 50-500 ppm, most preferably 50-100 ppm.

[0037] Preferably, the peroxidation process is carried out at a temperature of 20° C. to 100° C., in the case of neat monochloroacetic acid preferably at a temperature of 70-100° C., in the case of water-diluted monochloroacetic acid it is preferably 20-80° C.

[0038] In a preferred industrial scale embodiment, peroxycarboxylic acid in the form of an aqueous solution is added to the distilled monochloroacetic acid stream from the distillation unit in a suitable weight ratio to the weight of the monochloroacetic acid.

[0039] The probable cause of coloration of crude MCAA is trace contaminants of an organic nature, difficult to identify by analytical methods, sensitive to high temperature and formed, in particular in the initial period after replacement and/or when the fresh catalyst of the hydrogenation process is put into use, when the fresh hydrogenation catalyst shows very high activity and relatively low selectivity.

[0040] In the method according to the invention, the trace organic impurities are peroxidated with the peroxycarboxylic acid. Surprisingly, the expedient peroxidation of the crude MCAA according to the invention ultimately completely eliminates the undesirable colored oxidation intermediates from the finished product.

[0041] The use of such a solution allows to eliminate the phenomenon of aging of the product, which is manifested by a gradual change of color in the case of the liquid form from colorless to light yellow or light brown or light gray, and in the case of the solid form from white to light yellow or light brown or light pink.

[0042] As it is the last step in the production of monochloroacetic acid, it is possible to use aqueous solutions of peroxycarboxylic acids. Thanks to this, all risks related to their introduction at earlier stages of production have been eliminated.

[0043] Laboratory studies of the thermal stability of monochloroacetic acid products show that to obtain colorless, time-stable MCAA products, it is enough to add to the undiluted form of monochloroacetic acid obtained from the distillation process and stored in the operational tank in the case of: the undiluted form of MCAA in the amount of 50 to 1000 ppm, and in the case of the diluted form of MCAA from 50 to 1000 ppm of peroxycarboxylic acid to achieve complete thermal stability of the final product.

[0044] In the event that more peroxycarboxylic acid than necessary was added to the system, the system would remain stable and the final product would not be adversely affected, since the peroxycarboxylic acid is inert towards both monochloroacetic acid and dichloroacetic acid without changing their concentrations in the end products over time, which allows to always receive the product within the desired specification range.

[0045] The following examples illustrate the present invention.

EXAMPLES

[0046] The thermal stabilization test of monochloroacetic acid is performed on the test stand shown in FIG. 1, consisting of the following elements: [0047] 1. A jacketed mixing tank with a volume of 1 dm.sup.3 equipped with a mechanical stirrer, temperature control in the range of 10° C.-100° C., nitrogen blanket. [0048] 2. Monochloroacetic acid dispenser [0049] 3. Peracetic acid dispenser [0050] 4. Circulation pumps with a work efficiency in the range of 0.1 dm.sup.3/h-5 dm.sup.3/h, [0051] 5. Sampling point [0052] 6. Needle valve for check-regulating the nitrogen blanket [0053] 7. Needle valve regulating the nitrogen blanket [0054] 8. Digital pressure gauge to control the nitrogen blanket [0055] 9. Granulation belt [0056] 10. Operational tank 1 [0057] 11. Operational tank 2 [0058] 12. Demineralized water dispenser [0059] 13. Static mixer [0060] 14. Operational tank 3

[0061] Before filling the mixing tank (1), the jacket heating is activated to heat the tank walls, and the nitrogen blanket is activated, which is controlled by two needle valves (6 and 7) and a digital pressure gauge (8). After the walls of the mixing tank (1) have heated up, monochloroacetic acid at a temperature of 70-100° C. is introduced into the reactor through the dispenser (2). After the mixing tank (1) is full, the mechanical stirrer is started. Then, an aqueous peroxycarboxylic acid solution is introduced through the dispenser (3). Then, after obtaining a homogeneous mixture, the circulation pump (4) is turned on to be able to control the color change of monochloroacetic acid under the influence of peroxycarboxylic acid by taking a sample through the sampling point (5). When monochloroacetic acid acquires the appropriate color, it is sent through the pump (4) to one of three nodes: [0062] 1. If the final product is to be a solid monochloroacetic acid in the form of flakes, monochloroacetic acid is dosed through the pump (4) to the granulating belt (9), where the production of monochloroacetic acid takes place and the product in the form of a flakes is stored in the operational tank (10) at ambient temperature. [0063] 2. If the end product is to be a liquid monochlorocotic acid, undiluted monochloroacetic acid is sent through the pump (4) to the operational tank (11), where the temperature is maintained at 70° C. [0064] 3. If the final product is to be a liquid monochlorocotic acid diluted with water, the monochloroacetic acid is sent through the pump (4) to the static mixer (13), where it is diluted to the appropriate concentration by demineralized water dosed by the dispenser (12). The finished product is stored in the operational tank (14), where the temperature is maintained at 25-40° C.

Example 1—Monochloroacetic Acid in Undiluted Liquid Form

[0065] The study of thermal stability of undiluted monochloroacetic acid begins with heating the mixing tank to a temperature of 70° C. in order to prevent the process of monochloroacetic acid crystallization on its walls, and creating a nitrogen blanket with a pressure of 0.01 bar (g). 1000 g of monochloroacetic acid at a temperature of 70° C., for which a color of 12 units on Hazen scale was measured, was placed in the mixing tank. Then, the mechanical stirrer is started and the acid temperature is maintained at 70° C., then 3.33 g of a 15% aqueous solution of peracetic acid is dosed into the mixing tank. Then, after obtaining the homogeneous mixture, the circulation pump is started and acid samples are taken through the sampling point at regular intervals. After obtaining a stable color of 36 units on Hazen scale, the monochloroacetic acid is sent by a pump to the operational tank, where it is then kept at 70° C. for a period of 7 days. After this period, the color of the product is determined again.

[0066] Parallel to the above test, a similar test is carried out on the same test stand, with the difference that no peracetic acid is added to the control sample of monochloroacetic acid.

[0067] The color measurement results are summarized in Table 2.

TABLE-US-00002 TABLE 2 Color change of undiluted liquid MCAA when stored at elevated temperature (70° C.) for 7 days. The color level was determined on Hazen scale. The color of the product was measured at the beginning of the test (measurement 0) and after the selected test days (i.e., days 1 and 7). Color in Hazen units - incubation at 70° C., day of measurement Product: molten MCAA 0 1 7 CONTROL SAMPLE <60 >60 >60 100% MCAA (0) - peracetic acid free TEST SAMPLE <60 <60 <60 100% MCAA (1) - with peracetic acid eq = 500 ppm

Example 2—Solid Monochloroacetic Acid

[0068] The study of thermal stability of undiluted monochloroacetic acid begins with heating the mixing tank to the temperature of 70° C. in order to prevent the process of monochloroacetic acid crystallization on its walls, and creating a nitrogen blanket with a pressure of 0.01 bar (g). 1000 g of monochloroacetic acid at a temperature of 70° C., for which the color of 44 units on Hazen scale was measured, was placed in the mixing tank. Then, the mechanical stirrer is started and the acid temperature is maintained at 70° C., then 2.00 g of a 15% aqueous solution of peracetic acid is dosed into the mixing tank. Then, after obtaining the homogeneous mixture, the circulation pump is started and acid samples are taken through the sampling point at regular intervals. After obtaining a stable color at the level of 54 units on Hazen scale, monochloroacetic acid is sent by a pump to the granulating belt, where the monochloroacetic acid is packaged and the solid acid is produced in the form of flakes, which are then stored in a foil bag in the operational tank at ambient temperature. Monochloroacetic acid flakes are stored in a foil bag for 4 weeks at ambient temperature. After this period, the chloroacetic acid flakes are dissolved in water so as to obtain a liquid aqueous solution with 80% MCAA content, and the color of the resulting solution was then measured, which was 19 units on Hazen scale.

[0069] Parallel to the above test of test samples with the use of the same test apparatus, an analogous test is carried out with the difference that no peracetic acid is added to the control sample of monochloroacetic acid.

[0070] The color measurement results are summarized in Table 3.

TABLE-US-00003 TABLE 3 Color change of liquid 80% MCAA solution during incubation at elevated temperature (40° C.) for 7 days, prepared from flakes after storage at room temperature for 28 days. The color level was determined on Hazen scale. Color in Hazen units - incubation at 40° C., Shelf life MCAA day of measurement Product: MCAA flakes flakes in solid form 0 1 7 CONTROL SAMPLE 28 days at ambient >20 >20 >20 MCAA flakes temperature diluted to 80% MCAA - without peracetic acid TEST SAMPLE 28 days at ambient <20 <20 <20 MCAA flakes temperature diluted to 80% MCAA - with peracetic acid eq = 300 ppm

Example 3—Monochloroacetic Acid in Liquid Form, Diluted with Water

[0071] The study of thermal stability of monochloroacetic acid in a liquid, diluted form begins with heating the mixing tank to the temperature of 70° C. in order to prevent the process of monochloroacetic acid crystallization on its walls, and creating a nitrogen blanket with a pressure of 0.01 bar (g). 800 g of monochloroacetic acid at a temperature of 70° C., for which the color of 39 units on Hazen scale was measured, was placed in the mixing tank. Then, the mechanical stirrer is started and the acid temperature is maintained at 70° C., and then 0.533 g of a 15% aqueous peracetic acid solution is dosed into the mixing tank. Then, after obtaining the homogeneous mixture, the circulation pump is started and acid samples are taken through the sampling point at regular intervals. After obtaining a stable color of 44 units on Hazen scale, the monochloroacetic acid is pumped to a static mixer where it is mixed with 200 g of demineralized water dispensed by a dispenser. The chloroacetic acid diluted in this way is sent to the operational tank for which the color of 15 units on Hazen scale was measured. Then it is kept at 40° C. for 7 days. After this period, the color of the product is determined again.

[0072] Parallel to the above test, a similar test is carried out on the same test stand, with the difference that no peracetic acid is added to the control sample of monochloroacetic acid.

[0073] The results of the color measurements are summarized in Table 4.

TABLE-US-00004 TABLE 4 Color change of 80% MCAA during storage at elevated temperature (40° C.) for 7 days. The color level was determined on Hazen scale. The color of the product was measured at the beginning of the test (measurement 0) and after the selected test days (i.e., days 1 and 7). Color in Hazen units - incubation at 40° C., day of measurement Product: 80% MCAA 0 1 7 80% MCAA (1) - without <20 >20 >20 peracetic acid 80% MCAA (2) - with <20 <20 <20 peracetic acid eq = 100 ppm